This application discloses a novel tension control apparatus and tensioning method for a cable drag conveyor. A cable drag conveyor is used to convey powders and other particulate matter by entraining the particulate matter between discs. Such conveyors typically include an endless wire rope assembly upon which the disks are fastened and used for carrying the particulate matter. The rope assembly is typically carried along a circuit defined by a straight and curved tube or pipe, with sections for product in feed and discharge, an enclosed head and tail pulleys, and idler corners in various configurations on the empty return side of the conveyor to complete the circuit. The housings are interconnected by two tubes through which the rope assembly travels as it moves around the head and tail pulleys. As the conveyor operates, forces are exerted on the rope assembly that can cause the rope assembly to stretch. These forces are created by normal wear on the conveyor, the weight of the material being conveyed along the rope assembly, and similar other factors. The rope assembly can stretch to the point that a conventional tensioning device cannot exert adequate tension on the rope.
Cable drag conveyors typically travel in the range of 150 ft./min (46 m/min) and are particularly useful in conveying relatively fragile material such as coffee and grains with damage. This type of conveyor is distinguished from aero-mechanical conveyors, which travel at much higher speeds, for example, up to 1200 ft./min (367 m/min) and create an air stream in which the material is entrained.
Prior art manual tension adjusting mechanisms exist for moving the head and tail pulley assemblies relative to each other to maintain the correct amount of tension on the rope assembly. For example, some traditional prior art tension adjusting mechanisms rely on clamps which fasten the semi-circular housings to the tubes. Tension on the rope assembly is adjusted by loosening the bolts that hold the clamps in place and sliding one or both of the housings inwardly or outwardly relative to the tubes. Another prior art method of adjusting the tension on the rope assembly involves moving the drive or driven pulley together with the housing. Regardless of which prior art method is employed, adjusting the tension by moving the housings relative to the conveyor tubes is a manual operation. In addition, the discharge end of the equipment is frequently inaccessible, making access to the tube joining clamps challenging, and according to each method, the clamps have to be slackened and re-tightened. Furthermore, once the tension has been adjusted, there is no guarantee that the tubes and the connecting spigots leading to the housings will be properly aligned, which makes jamming a possible cause of failure.
Other devices and methods for controlling tension in conveyors are disclosed in applicant's U.S. Pat. Nos. 7,798,313 and 6,598,736.
The invention of the present application overcomes the problems inherent to the prior art described above by providing a tension control apparatus for use on a cable drag conveyor that adjusts tension without moving the housings and without requiring any significant manual intervention. The tension control apparatus of the present invention preferably uses a constant load device such as a pneumatic cylinder that applies a pre-selected amount of tension on the rope assembly.